Process for superheated steam

ABSTRACT

Disclosed is a process for the preparation of superheated of steam by transferring heat from at least a fraction of a high pressure steam to a lower pressure steam to produce a superheated, lower pressure steam. The high pressure steam can be generated by recovering heat from a heat producing chemical process such as, for example, the partial oxidation of carbonaceous materials. The lower pressure steam can be generated by reducing the pressure of a portion of the high pressure steam or by recovering heat from one or more chemical processes. The superheated, lower pressure steam may used to generate electricity in a steam turbine, operate a steam turbine drive, or as a heat source. Also disclosed is a process for driving a steam turbine using superheated steam produced by the process of the invention.

FIELD OF THE INVENTION

This invention relates in general to a process for the preparation ofsuperheated steam. More particularly, this invention relates to aprocess for the preparation of superheated steam by transferring heatfrom at least a fraction of a high pressure steam to a lower pressuresteam to produce a superheated, lower pressure steam. The lower pressuresteam can be generated by reducing the pressure of a portion of a highpressure steam or by recovering heat from one or more chemicalprocesses. The superheated, lower pressure steam may used to generateelectricity in a steam turbine, operate a steam turbine drive, or as aheat source.

BACKGROUND OF THE INVENTION

Many industrially significant chemical reactions are highly exothermicand the heat of reaction is used to generate steam. Examples of steamgenerating chemical processes include ethylene oxide production bypartial oxidation of ethylene, methanol production from synthesis gas,gasification or partial oxidation of carbonaceous materials,formaldehyde production from methanol, production of Fischer-Tropschhydrocarbons or alcohols from synthesis gas, ammonia production fromhydrogen and nitrogen, and the water-gas shift reaction to producehydrogen from carbon monoxide and water. In such processes, thesaturated steam, that is steam at its dew point for the prevailingpressure and temperature conditions, typically is generated by coolingof reactors or as a post-reaction heat removal technique. The amount ofsteam generated, however, often can exceed the heating needs within thebattery limits of the process itself.

In addition to its use as a heating medium, steam thus generated can beused as a source of work to generate electricity in a turbogenerator oras motive force to drive machinery such as a turbine-driven compressoror pump. During the expansion process in turbomachinery, a portion ofthe enthalpy of the inlet high pressure steam is converted to motivework, and is converted to a lower pressure, cooler steam that exits theturbine. Such processes are described for example in “Steam, ItsGeneration and Use”, Babcock and Wilcox Co, New York, 37^(th) Edition,1960, Chapter 10, pp. 10-1 to 10-22.

Although either saturated or superheated steam can be used inturbomachinery, it is well-known in the art that the thermodynamicefficiency (useful work energy out divided by enthalpy input) isproportional to the amount of superheat. An example of this phenomenonis shown in FIG. 10, pg. 10-8, of the above reference, in which thethermodynamic efficiency is 39.7% for the expansion of 100 barasaturated steam across a steam turbine to 0.485 bara. By contrast, a42.6% efficiency is achieved for the same pressure differential with thesteam superheated by 167° C. prior to introduction to the turbine.

Often during the expansion process, a fraction of the vaporous steamfeed condenses and forms liquid water. Generation of liquid water withinthe turbine results in formation of water droplets, these dropletsstrike the turbine blades with great force and cause erosive wear overtime. The amount of liquid water generated in the turbine is a complexfunction of the degree of superheat of the inlet steam, the pressuredifferential across the turbine, and the mechanical efficiency of theturbine. For example, if 100 bara saturated steam is expanded across asteam turbine to 0.485 bara at 85% efficiency, the quality (i.e., thefraction of a wet steam that is in the vapor state) of the outlet steamis 73.4%, whereas introduction into the same steam turbine of 100 barasaturated steam superheated by 200° C. results in an outlet quality of87.5%. Alternatively if 50 bara saturated steam is expanded to 0.485bara, the outlet steam quality is 74.8%. If the degree of superheat ishigh enough no liquid water will form. For a 100 bara to 0.485 baraexpansion at 85% mechanical efficiency, the outlet quality is 100% ifthe inlet steam is superheated by at least 495° C.

It is well known that the use of saturated steam as the motive force inturbomachinery causes increased erosive wear and resulting highermaintenance costs as compared to the use of superheated steam.Typically, an outlet quality of at least 75% is preferred, an outletquality of 85% or higher is more preferable. With many steam generatingchemical processes, however, no high temperature heat source ofsufficient quantity is available to superheat the steam thus generated.Although it is possible to burn a portion of either the raw material,product, by-product streams, or an externally supplied fuel to provide ahigh temperature heat source useful for superheating steam, this methodis hampered by the wasteful consumption of raw materials, insufficientavailability of by-products, or requires the purchase of expensive fuelsand additional capital for the combustor and associated heat exchangers.Thus, there is a need to provide a means for superheating steam fromsteam generating chemical processes without undue capital or fuel costs.

SUMMARY OF THE INVENTION

In one embodiment of the invention, I have discovered that high pressuresteam generated in a chemical process may be conveniently andeconomically used to produce a superheated steam by reducing thepressure of a portion of the high pressure steam to produce a lowerpressure steam and using the remaining portion of the high pressuresteam to superheat the lower pressure steam. Accordingly, a process forthe preparation of superheated steam is set forth comprising:

-   (a) recovering heat from at least one chemical process to produce a    high pressure steam;-   (b) reducing the pressure of a portion of the high pressure steam of    step (a) to produce a lower pressure steam and a remaining portion    of the high pressure steam; and-   (c) transferring heat from at least a fraction of the remaining    portion of the higher pressure steam of step (b) to the lower    pressure steam to produce a superheated steam from the lower    pressure steam.    The process of the invention may be used in conjunction with a    variety of chemical processes. For example, the high pressure steam    may be generated from at least one chemical process selected from    partial oxidation, carbonylation, hydrogenation, and homologation.    Representative examples of chemical processes include, but are not    limited to, gasification of carbonaceous materials to produce    synthesis gas, hydrogenation of carbon monoxide or carbon dioxide to    produce methanol, partial oxidation of ethylene to produce ethylene    oxide, steam reforming of methane to produce synthesis gas, partial    oxidation of methanol to produce formaldehyde, production of    Fischer-Tropsch hydrocarbons or alcohols from synthesis gas, ammonia    production from hydrogen and nitrogen, autothermal reforming of    carbonaceous feedstocks to produce synthesis gas, hydrogenation of    dimethyl terephthalate to cyclohexanedimethanol, carbonylation of    methanol to acetic acid, the water-gas shift reaction to produce    hydrogen and carbon dioxide from carbon monoxide and water, or a    combination thereof. The superheated, lower pressure steam can be    used to generate electricity in a steam turbine, operate a steam    turbine drive, or as a heat source.

The process of the invention may be used advantageously with processesthat produce syngas by the partial oxidation of carbonaceous materials.Such processes, either alone or in combination with other chemicalprocesses, frequently produce abundant or excessive amounts of highpressure steam but are deficient in superheated steam. Hence, anotheraspect of the invention is a process for the preparation of superheatedsteam, comprising:

-   (a) reacting a carbonaceous material with oxygen, water, or carbon    dioxide to produce heat and a syngas stream comprising hydrogen,    carbon monoxide, and carbon dioxide;-   (b) recovering the heat to produce a high pressure steam; and-   (c) transferring heat from at least a fraction of the high pressure    steam of step (b) to a lower pressure steam by indirect heat    exchange to produce a superheated steam from the lower pressure    steam.    The carbonaceous material may include, but is not limited to,    methane, petroleum residuum, carbon monoxide, coal, coke, lignite,    oil shale, oil sands, peat, biomass, petroleum refining residues,    petroleum cokes, asphalts, vacuum resid, heavy oils, or combinations    thereof, and can be reacted with oxygen in a gasifier, partial    oxidizer, or reformer. The lower pressure steam may be obtained by    reducing the pressure of a portion of the high pressure steam or by    recovery of heat from at least one chemical process such as, for    example a water-gas shift reaction, hydrogenation of carbon monoxide    to produce methanol, hydrogenation of nitrogen to produce ammonia,    carbonylation of methanol to produce acetic acid, Fischer-Tropsch    processes, production of alkyl formates from carbon monoxide and    alcohols, and combinations thereof.

In yet another aspect of the invention, the high pressure steam can beproduced by recovering heat from a gasifier and can be used to generatea superheated steam which, in turn, can be used to drive a steamturbine. Thus, the invention also provides a process for driving a steamturbine, comprising:

-   (a) reacting a carbonaceous material with oxygen in a gasifier to    produce heat and a syngas stream comprising hydrogen, carbon    monoxide, and carbon dioxide;-   (b) recovering the heat to produce a high pressure steam;-   (c) transferring heat from at least a fraction of the high pressure    steam of step (b) to a lower pressure steam by indirect heat    exchange to produce a superheated steam from the lower pressure    steam; and-   (d) passing the superheated steam to a steam turbine.    The steam turbine can be used to drive a generator to produce    electricity or drive a gas compressor. For example, the gasifier and    turbine may be part of an integrated gasification combined cycle    (abbreviated herein as “IGCC”) power plant, which may further    comprise a chemical producing plant to convert excess syngas into    fuel or salable chemicals.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-5 are schematic flow diagrams that illustrate severalembodiments of the process of the invention.

DETAILED DESCRIPTION

In a general embodiment, the present invention provides a novel processfor superheating steam in which high pressure steam generated in achemical process can be used advantageously to produce a superheatedsteam without the use of an external heat source. It has been discoveredthat a portion of the high pressure steam may be reduced in pressure toproduce a lower pressure steam and that the remaining portion of thehigh pressure steam can be used to superheat the lower pressure steam toproduce a superheated steam. Accordingly, a process for the preparationof superheated steam is set forth comprising:

-   (a) recovering heat from at least one chemical process to produce a    high pressure steam;-   (b) reducing the pressure of a portion of the high pressure steam of    step (a) to produce a lower pressure steam and a remaining portion    of the high pressure steam; and-   (c) transferring heat from at least a fraction of the remaining    portion of the higher pressure steam of step (b) to the lower    pressure steam to produce a superheated steam from the lower    pressure steam.    The high pressure steam can be generated from a variety of chemical    processes such as, for example, partial oxidation, carbonylation,    hydrogenation, and homologation. Some representative examples of    chemical processes include, but are not limited to, gasification of    carbonaceous materials to produce synthesis gas, hydrogenation of    carbon monoxide or carbon dioxide to produce methanol, partial    oxidation of ethylene to produce ethylene oxide, steam reforming of    methane to produce synthesis gas, partial oxidation of methanol to    produce formaldehyde, production of Fischer-Tropsch hydrocarbons or    alcohols from synthesis gas, ammonia production from hydrogen and    nitrogen, autothermal reforming of carbonaceous feedstocks to    produce synthesis gas, hydrogenation of dimethyl terephthalate to    cyclohexanedimethanol, carbonylation of methanol to acetic acid,    water-gas shift reaction to produce hydrogen and carbon dioxide from    carbon monoxide and water, or a combination thereof. The    superheated, lower pressure steam may used to generate electricity    with a steam turbine, operate a steam turbine drive, or as a heat    source.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe following specification and attached claims are approximations thatmay vary depending upon the desired properties sought to be obtained bythe present invention. At the very least, each numerical parametershould at least be construed in light of the number of reportedsignificant digits and by applying ordinary rounding techniques.Further, the ranges stated in this disclosure and the claims areintended to include the entire range specifically and not just theendpoint(s). For example, a range stated to be 0 to 10 is intended todisclose all whole numbers between 0 and 10 such as, for example 1, 2,3, 4, etc., all fractional numbers between 0 and 10, for example 1.5,2.3, 4.57, 6.113, etc., and the endpoints 0 and 10. Also, a rangeassociated with chemical substituent groups such as, for example, “C₁ toC₅ hydrocarbons”, is intended to specifically include and disclose C₁and C₅ hydrocarbons as well as C₂, C₃, and C₄ hydrocarbons.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements and/or calculations.

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” include their plural referents unless the contextclearly dictates otherwise. For example, references to a “heatexchanger,” or a “steam flow,” is intended to include the one or moreheat exchangers, or steam flows. References to a composition or processcontaining or including “an” ingredient or “a” step is intended toinclude other ingredients or other steps, respectively, in addition tothe one named.

The term “containing” or “including”, as used herein, is intended to besynonymous with the term “comprising”; that is at least the namedcompound, element, particle, or process step, etc., is present in thecomposition or article or process, but does not exclude the presence ofother compounds, catalysts, materials, particles, process steps, etc,even if the other such compounds, material, particles, process steps,etc., have the same function as what is named, unless expressly excludedin the claims.

It is also to be understood that the mention of one or more processsteps does not preclude the presence of additional process steps beforeor after the combined recited steps or intervening process steps betweenthose steps expressly identified. Moreover, the lettering of processsteps or ingredients is a convenient means for identifying discreteactivities or ingredients and the recited lettering can be arranged inany sequence, unless otherwise indicated.

The process of the invention comprises recovering heat from a least onechemical process to produce a high pressure steam. The high pressuresteam used in the instant invention may be saturated or superheated. Therecovery of heat may be from any chemical process which producessufficient heat to produce steam having a pressure of about 4 bara. Theterm bara, as used herein means “bar absolute”. Steam at about 4 bara orhigher may be dropped in pressure and superheated to useful levels bymeans laid out in this invention. In such processes, typically saturatedsteam, i.e., steam at its dew point for the prevailing pressure andtemperature conditions, is generated by cooling of reactors or as apost-reaction heat removal technique. Alternatively, the lower pressuresteam derived from the steam generating chemical process may besuperheated, but with a degree of superheat lower than desired. In thislatter case, the lower pressure steam may be subjected to the steps ofthe instant invention to further increase its degree of superheat.

Representative examples of such heat producing chemical processesinclude, but are not limited to, partial oxidation, carbonylation,hydrogenation, water-gas shift reaction, steam reforming, andhomologation. More specific, non-limiting examples of chemical processeswhich may be used in the process of the invention include gasificationof carbonaceous materials to produce synthesis gas, hydrogenation ofcarbon monoxide or carbon dioxide to produce methanol, partial oxidationof ethylene to produce ethylene oxide, steam reforming of methane toproduce synthesis gas, partial oxidation of methanol to produceformaldehyde, production of Fischer-Tropsch hydrocarbons or alcoholsfrom synthesis gas, ammonia production from hydrogen and nitrogen,autothermal reforming of carbonaceous feedstocks to produce synthesisgas, hydrogenation of dimethyl terephthalate to cyclohexanedimethanol,carbonylation of methanol to acetic acid, water-gas shift reaction toproduce hydrogen and carbon dioxide from carbon monoxide and water, or acombination thereof.

The chemical process can, for example, include the partial oxidation ofa carbonaceous material by reaction with oxygen, water, or carbondioxide to produce heat and syngas stream comprising hydrogen, carbonmonoxide, and carbon dioxide. The term “carbonaceous”, as used herein,means the various, suitable feedstocks that contain carbon and isintended to include gaseous, liquid, and solid hydrocarbons,hydrocarbonaceous materials, and mixtures thereof. Substantially anycombustible carbon-containing organic material, or slurries thereof, maybe included within the definition of the term “carbonaceous”. Solid,gaseous, and liquid feeds may be mixed and used simultaneously; andthese may include paraffinic, olefinic, acetylenic, naphthenic, andaromatic compounds in any proportion. Also included within thedefinition of the term “carbonaceous” are oxygenated carbonaceousorganic materials including carbohydrates, cellulosic materials,aldehydes, organic acids, alcohols, ketones, carbon monoxide, oxygenatedfuel oil, waste liquids and by-products from chemical processescontaining oxygenated carbonaceous organic materials, and mixturesthereof. The term “syngas”, as used herein, is intended to be synonymouswith the term “synthesis gas” and understood to mean a gaseous mixtureof varying composition comprising primarily hydrogen, carbon monoxide,and various impurities depending on its method of generation. Thepartial oxidation process, for example, may comprise steam or carbondioxide reforming of carbonaceous materials such as, for example,natural gas or petroleum derivatives. These processes are well known topersons skilled in the art and are practiced commercially. In anotherexample, the partial oxidation process may comprise gasification ofcarbonaceous materials such as, for example, methane, coal, coke,lignite, oil shale, oil sands, peat, biomass, petroleum refiningresidues, petroleum cokes, asphalts, vacuum resid, heavy oils, orcombinations thereof, by reaction with oxygen to produce syngas andheat. The term “oxygen”, as used herein, is intented to includesubstantially pure gaseous, elemental oxygen, or any reactiveO₂-containing gas, such as air, substantially pure oxygen having greaterthan about 90 mole percent oxygen, or oxygen-enriched air having greaterthan about 21 mole percent oxygen. Substantially pure oxygen ispreferred in the industry. To obtain substantially pure oxygen, air iscompressed and then separated into substantially pure oxygen andsubstantially pure nitrogen in an air separation plant. Such plants areknown in the industry.

Any one of several known gasification processes can be incorporated intothe process of the instant invention. These gasification processesgenerally fall into broad categories as laid out in Chapter 5 of“Gasification”, (C. Higman and M. van der Burgt, Elsevier, 2003).Examples are moving bed gasifiers such as the Lurgi dry ash process, theBritish Gas/Lurgi slagging gasifier, the Ruhr 100 gasifier; fluid-bedgasifiers such as the Winkler and high temperature Winkler processes,the Kellogg Brown and Root (KBR) transport gasifier, the Lurgicirculating fluid bed gasifier, the U-Gas agglomerating fluid bedprocess, and the Kellogg Rust Westinghouse agglomerating fluid bedprocess; and entrained-flow gasifiers such as the Texaco, Shell,Prenflo, Noell, E-Gas (or Destec), CCP, Eagle, and Koppers-Totzekprocesses. The gasifiers contemplated for use in the process may beoperated over a range of pressures and temperatures between about 1 toabout 103 bar absolute and 400° C. to 2000° C., with preferred valueswithin the range of about 21 to about 83 bara and temperatures between500° C. to 1500° C. Depending on the carbonaceous or hydrocarbonaceousfeedstock used therein and type of gasifier utilized to generate thegaseous carbon monoxide, carbon dioxide, and hydrogen, preparation ofthe feedstock may comprise grinding, and one or more unit operations ofdrying, slurrying the ground feedstock in a suitable fluid (e.g., water,organic liquids, supercritical or liquid carbon dioxide). Typicalcarbonaceous materials which can be oxidized to produce syngas include,but are not limited to, petroleum residuum, bituminous, subbituminous,and anthracitic coals and cokes, lignite, oil shale, oil sands, peat,biomass, petroleum refining residues, petroleum cokes, and the like.

The heat produced in the chemical process may be recovered by any heatexchange means known in the art including, but not limited to, radiantheat exchange, convective heat exchange, or a combination thereof toproduce a high pressure steam. For example, in gasification processes,the heat may be recovered using at least one of the following types ofheat exchangers selected from steam generating heat exchangers (i.e.,boilers), wherein heat is transferred from the syngas to boil water;shell and tube; plate and frame; spiral; or combinations of one or moreof these heat exchangers. For example, the heat from the gasificationprocess can be recovered by radiant heat exchange. Convective heating orcooling occurs by transfer of heat from one point within a fluid (gas orliquid) by mixing of one portion of the fluid with another portion. Atypical indirect heat exchange process will involve transfer of heat toor from a solid surface (often a tube wall) to a fluid element adjacentto the wall, then by convection into the bulk fluid phase. Radiant heattransfer involves the emission of electromagnetic energy from matterexcited by temperature and absorption of the emitted energy by othermatter at a distance from the source of emission. For example, the rawsyngas leaves the gasifier and can be cooled in a radiant syngas cooler.The recovered heat is used to generate high pressure steam. Radiantsyngas coolers are known in the art and may comprise, for example, atleast one ring of vertical water cooled tubes, such as shown anddescribed in U.S. Pat. Nos. 4,310,333 and 4,377,132.

The use of multiple steam generating heat exchangers also iscontemplated to be within the scope of the instant invention. Steam andcondensate generated within gas cooling zones may embody one or moresteam products of different pressures. The gas cooling zones optionallymay comprise other absorption, adsorption, or condensation steps forremoval of trace impurities, e.g., such as ammonia, hydrogen chloride,hydrogen cyanide, and trace metals such as mercury, arsenic, and thelike.

The high pressure steam can be saturated or superheated and typicallywill have a pressure of about 4 to about 140 bara. In another example,the high pressure steam can have a pressure of about 20 to about 120bara. A portion of the high pressure steam can be reduced in pressure toproduce a lower pressure steam and a remaining portion of the highpressure steam. If the high pressure steam is superheated, the lowerpressure steam also may be superheated but to an insufficient degree.The terms “high pressure steam” and “lower pressure steam”, as usedherein, are intended to indicate the relative and not absolute pressuresof the various steam flows of the present invention. As used herein inthe context of the claims and description, “high pressure steam” isintended to mean steam from which heat is transferred, wherein the term“lower pressure steam” means steam to which heat is transferred.Representative examples of portions or fractions of the high pressuresteam that can be let down or expanded to produce the lower pressuresteam are about 40 to about 95 mass %, about 50 to about 80 mass %,about 60 to about 95 mass %, about 70 to about 95 mass %, and about 75to about 95 mass %, based on the total mass of the high pressure steam.Any means known in art may be used to reduce the pressure of the highpressure steam; however, it will be evident to persons skilled in theart that generation of a lower pressure steam will involve expanding aportion of the high pressure steam. For example, the process of theinvention may comprise expanding a portion of the high pressure steamthrough a valve, a turbine, or a combination thereof. Typically, theratio of the pressures of the high to lower pressure steams will be140:1 to 1.5:1, 100:1 to 2:1, 25:1 to 2:1, or 10:1 to 2:1. In addition,the higher pressure steam and the lower pressure steam typically willhave a difference in water saturation temperature of about 40° C. toabout 250° C.

According to the invention, heat can be transferred from at least afraction of the remaining portion of the higher pressure steam to thelower pressure steam to produce a superheated steam from the lowerpressure steam or increase the degree of superheat if the lower pressuresteam is already superheated. The term “superheated”, as used herein, isunderstood to mean that the lower pressure steam is heated above its dewpoint at a given pressure or, if it is already superheated, its degreeof superheat increased. The amount of superheat typically is at least40° C. Other examples of superheat are from about 20° C. to about 250°C., from about 50° C. to, at least 150° C., and at least 50° C. to about125° C. The heat exchange between the low and high pressure steam canoccur by indirect methods using any device known in the art, includingshell and tube heat exchangers, plate and frame exchangers, spiralexchangers, and compact plate-fin exchangers. “Indirect heat exchange”,as used herein, is understood to mean the exchange of heat across asurface without mixing as opposed to “direct heat exchange” in which thehigh and lower pressure steam are mixed together. Typically, the heatexchanger is of shell and tube design, with the condensing high pressuresteam on the shell side. The heat exchange process may be implemented asmultiple heat exchangers in series.

The approach temperature, i.e., the temperature difference between thesuperheated lower pressure steam and the temperature of the highpressure steam, is typically from about 1 to about 20° C. Other examplesof approach temperatures are from about 1 to about 10° C. and from about1 to about 5° C. Although, desired to be as low as possible, thepractical limit to the approach temperature is strongly dictated byeconomics. The area required for heat transfer increases logarithmicallywith a decrease in approach temperature.

The lower pressure steam subjected to heat exchange against theremaining portion of high pressure steam may have a quality less than orequal to unity depending on the temperature and pressure conditions ofthe inlet high pressure steam as well as the outlet pressure. The term“quality”, as used herein with respect to steam, means the mass fractionof vapor in the vapor phase with respect to the total mass of water andvapor in the steam. If desired, liquid water may be removed from thelower pressure steam by any means known in the art such as described in“Phase Segregation”, Chapter 3, pp. 129-148, L. J. Jacobs and W. R.Penney, in Handbook of Separation Process Technology, R. W. Rousseau,ed., Wiley & Sons, 1987, including knockout pots, pipe separators, meshpads, centrifugal vanes, tangential entry separators, demister orcoalescer pads, wavy plates, packing, cyclone or venturi scrubbers,electrostatic precipitators, and the like.

The superheated, lower pressure steam generated in the instant inventionmay used to generate electricity in a steam turbine, operate a steamturbine drive, or as a heat source. Typically, the superheated, lowerpressure steam can be passed to a steam turbine where is used to supplymotive force to operate a compressor or a generator. When passed to asteam turbine, the degree of superheating of the lower pressure steamproduced in the process of the invention generally will produce outletquality of about 75% to about 100%. Other examples of outlet quality forthe steam exiting the steam turbine are about 80% to about 100% andabout 85% to about 100%.

The superheated steam process of the present invention, in particular,may be used in conjunction with processes that produce syngas by thepartial oxidation of carbonaceous materials such as, for example,gasification or steam reforming of methane. Such processes, either aloneor in combination with other chemical processes frequently produceabundant or excessive amounts of high pressure steam but are deficientin superheated steam. Therefore, another aspect of the invention is aprocess for the preparation of superheated steam, comprising:

-   (a) reacting a carbonaceous material with oxygen, water, or carbon    dioxide to produce heat and a syngas stream comprising hydrogen,    carbon monoxide, and carbon dioxide;-   (b) recovering the heat to produce a high pressure steam; and-   (c) transferring heat from at least a fraction of the high pressure    steam of step (b) to a lower pressure steam by indirect heat    exchange to produce a superheated steam from the lower pressure    steam.    The above process is understood to include the various embodiments    of heat recovery, heat exchange, steam pressure, steam turbines,    steam pressure reduction, steam quality, etc., as set forth    hereinabove in any combination. For example, the carbonaceous    material can be reacted with oxygen, water, or carbon dioxide to    produce heat and syngas stream comprising hydrogen, carbon monoxide,    and carbon dioxide. As described above, carbonaceous materials can    include, but are not limited to, methane, petroleum residuum, coal,    coke, lignite, carbon monoxide, oil shale, oil sands, peat, biomass,    petroleum refining residues, petroleum cokes, asphalts, vacuum    resid, heavy oils, or combinations thereof. The carbonaceous    material may be reacted in any type partial oxidation reactor known    in the art such as, for example, a gasifier, partial oxidizer, or    reformer. In one embodiment, for example, the carbonaceous material    can comprise methane and is reacted with water in a reformer. In    another example, the carbonaceous material may comprise coal or    petroleum coke and is reacted with oxygen in a gasifier. In yet    another example, the carbonaceous material comprises carbon monoxide    and is reacted with water in a water-gas shift reaction.

The heat produced by the syngas process can be recovered by radiant heatexchange, convective heat exchange, or a combination thereof to producea high pressure steam as described previously. The high pressure steamcan be saturated or superheated and, typically, will have a pressure ofabout 4 to 140 bara or, in another example, about 20 to 120 bara. Aportion of the high pressure steam can be reduced in pressure to producea lower pressure steam and a remaining portion of the high pressuresteam. Any means known in art may be used to reduce the pressure of thehigh pressure steam such as, for example, expanding a portion of thehigh pressure steam through a valve, a turbine, or combination thereof.

The lower pressure steam also may be produced by recovering heat fromone or more chemical processes in addition to and distinct from theprocess used to generate the high pressure steam. Representativeexamples of chemical processes which can be used include the water-gasshift reaction, hydrogenation of carbon monoxide or carbon dioxide toproduce methanol, hydrogenation of nitrogen to produce ammonia,carbonylation of methanol to produce acetic acid, Fischer-Tropschprocesses, production of alkyl formates from carbon monoxide andalcohols, and combinations thereof. Heat recovery can be accomplish byheat exchange techniques well known in the art and describedhereinabove. In another embodiment, the chemical process may include thewater-gas shift reaction, hydrogenation of carbon monoxide or carbondioxide to produce methanol, hydrogenation of nitrogen to produceammonia, or a combination thereof.

Typically the water-gas shift reaction is accomplished in a catalyzedfashion by methods known in the art. The water gas shift catalyst isadvantageously sulfur-tolerant. For example, such sulfur tolerantcatalysts can include, but are not limited to, cobalt-molybdenumcatalysts. Operating temperatures are typically 250° C. to 500° C.Alternatively, the water-gas shift reaction may be accomplished, aftersulfur removal from the carbon monoxide-containing reactant gas, usinghigh or low temperature shift catalysts. High temperature shiftcatalysts, for example iron-oxide promoted with chromium or copper,operate in the range of 300° C. to 500° C. Low temperature shiftcatalysts, for example, copper-zinc-aluminum catalysts, operate in therange of 200° C. to 300° C. Alternatively, the water-gas shift reactionmay be accomplished without the aid of a catalyst when the temperatureof the gas is greater than about 900° C. Because of the highlyexothermic nature of the water-gas shift reaction, steam may begenerated by recovering heat from the exit gases of the water-gas shiftreactor. The water-gas shift reaction may be accomplished in any reactorformat known in the art for controlling the heat release of exothermicreactions. Examples of suitable reactor formats are single stageadiabatic fixed bed reactors; multiple-stage adiabatic fixed bedreactors with interstage cooling, steam generation, or cold-shotting;tubular fixed bed reactors with steam generation or cooling; orfluidized beds.

The process of hydrogenation of carbon monoxide or carbon dioxide toproduce methanol can comprise any type of methanol synthesis plant thatis well known to persons skilled in the art, many of which are widelypracticed on a commercial basis. Most commercial methanol synthesisplants operate in the gas phase at a pressure range of about 25 to about140 bara using various copper based catalyst systems depending on thetechnology used. A number of different state-of-the-art technologies areknown for synthesizing methanol such as, for example, the ICI (ImperialChemical Industries) process, the Lurgi process, and the Mitsubishiprocess. Liquid phase processes are also well known in the art. Thus,the methanol process according to the present invention may comprise afixed bed methanol reactor, containing a solid or supported catalyst, orliquid slurry phase methanol reactor, which utilizes a slurried catalystin which metal or supported catalyst particles are slurried in anunreactive liquid medium such as, for example, mineral oil.

Typically, a syngas stream is supplied to a methanol reactor at thepressure of about 25 to about 140 bara, depending upon the processemployed. The syngas then reacts over a catalyst to form methanol. Thesyngas stream may or may not contain carbon dioxide in addition tohydrogen and carbon monoxide. The reaction is exothermic; therefore,heat removal is ordinarily required. The raw or impure methanol is thencondensed and may be purified to remove impurities such as higheralcohols including ethanol, propanol, and the like or, burned withoutpurification as fuel. The uncondensed vapor phase comprising unreactedsyngas feedstock typically is recycled to the methanol process feed.

The chemical process also can include the hydrogenation of nitrogen toproduce ammonia. This process can be carried by the Haber-Bosch processby means known in the art as exemplified by LeBlance et al in “Ammonia”,Kirk-Othmer Encyclopedia of Chemical Technology, Volume 2, 3rd Edition,1978, pp. 494-500.

In another embodiment of the invention, the chemical process cancomprise a Fischer-Tropsch process for the production of hydrocarbonsand alcohols from syngas as exemplified in U.S. Pat. Nos. 5,621,155 and6,682,711. Typically, the Fischer-Tropsch reaction may be effected in afixed bed, in a slurry bed, or in a fluidized bed reactor. TheFischer-Tropsch reaction conditions may include using a reactiontemperature of between 190° C. and 340° C., with the actual reactiontemperature being largely determined by the reactor configuration. Forexample, when a fluidized bed reactor is used, the reaction temperatureis preferably between 300° C. and 340° C.; when a fixed bed reactor isused, the reaction temperature is preferably between 200° C. and 250°C.; and when a slurry bed reactor is used, the reaction temperature ispreferably between 190° C. and 270° C.

In one embodiment, the process of the invention can be used in anintegrated combined cycle power plant in which coal or petroleum coke isreacted with oxygen to produce syngas and that syngas is used to fuel acombustion turbine for the generation of electricity and for thecoproduction of chemicals such as, for example, methanol,Fischer-Tropsch hydrocarbons, or ammonia. Recovery of heat from thegasification process can be used to generate a high pressure steamwhich, in turn, can be used to superheat a lower pressure steam that isgenerated by heat recovery from the chemical process or by reducing aportion of the pressure of the high pressure steam.

As described above, heat can be transferred from at least a fraction ofthe higher pressure steam to the lower pressure steam to produce asuperheated, lower pressure steam. The superheated lower pressure steammay used to generate electricity in a steam turbine, operate a steamturbine drive, or as a heat source. When passed to a steam turbine, thedegree of superheating of the lower pressure steam produced in theprocess of the invention generally will produce outlet quality of about75% to about 100%. Other examples of outlet quality for the steamexiting the steam turbine are about 80% to about 100% and about 85% toabout 100%.

The present invention also provides a process for driving a steamturbine using superheated, lower pressure steam produced by exchangingheat between a high pressure steam and a lower pressure steam asdescribed hereinabove. Thus, another aspect of the invention is aprocess for driving a steam turbine, comprising:

-   (a) reacting a carbonaceous material with oxygen in a gasifier to    produce heat and a syngas stream comprising hydrogen, carbon    monoxide, and carbon dioxide;-   (b) recovering the heat to produce a high pressure steam;-   (c) transferring heat from at least a fraction of the high pressure    steam of step (b) to a lower pressure steam by indirect heat    exchange to produce a superheated steam from the lower pressure    steam; and-   (d) passing the superheated steam to a steam turbine.    The above process is understood to include the various embodiments    of heat recovery, heat exchange, steam pressure, steam turbines,    steam pressure reduction, steam quality, etc., as set forth    hereinabove in any combination. Our process comprises reacting a    carbonaceous material such as, for example, petroleum residuum,    coal, coke, lignite, oil shale, oil sands, peat, biomass, petroleum    refining residues, petroleum cokes, asphalts, vacuum resid, heavy    oils, or combinations thereof, in a gasifier to produce a syngas    stream. Typically, the carbonaceous material will comprise coal or    petroleum coke and is reacted with oxygen or oxygen-containing gas    in a gasifier.

The heat produced by the gasification process can be recovered byradiant heat exchange, convective heat exchange, or a combinationthereof to produce a high pressure steam as described previously.Typically, the heat from the gasification process is recovered byradiant heat exchange. The high pressure steam can be saturated orsuperheated and, typically, will have a pressure of about 4 to 140 baraor, in another example, about 20 to 120 bara.

The lower pressure steam may be produced, as described above, byreducing the pressure of a portion of the high pressure steam or byrecovering heat from one or more chemical processes in addition to anddistinct from the process used to generate the high pressure steam.Representative examples of chemical processes which can be used havebeen described previously and include the water-gas shift reaction,hydrogenation of carbon monoxide or carbon dioxide to produce methanol,hydrogenation of nitrogen to produce ammonia, carbonylation of methanolto produce acetic acid, Fischer-Tropsch processes, production of alkylformates from carbon monoxide and alcohols, and combinations thereof. Inanother embodiment, the chemical process comprises a water-gas shiftreaction, hydrogenation of carbon monoxide or carbon dioxide to producemethanol, hydrogenation of nitrogen to produce ammonia, or a combinationthereof. In yet another embodiment, the chemical process compriseshydrogenation of carbon monoxide or carbon dioxide to produce methanol.In yet another embodiment, the chemical process may include thewater-gas shift reaction, hydrogenation of carbon monoxide or carbondioxide to produce methanol, hydrogenation of nitrogen to produceammonia, or a combination thereof. Heat recovery can be accomplish byheat exchange techniques well known in the art and describedhereinabove.

Heat can be transferred from at least a fraction of the higher pressuresteam of to the lower pressure steam to produce a superheated, lowerpressure steam as described previously. The superheated, lower pressuresteam may be passed to steam turbine, which may be used to drive agenerator to produce electricity or to drive a gas compressor. Thedegree of superheating of the lower pressure steam produced in theprocess of the invention generally will produce outlet quality of about75% to about 100%. Other examples of outlet quality for the steamexiting the steam turbine are about 80% to about 100% and about 85% toabout 100%.

Several embodiments of the process of the invention are are illustratedherein with particular reference to FIGS. 1-5. In the embodiment setforth in FIG. 1, a portion of the high pressure steam flowing in conduit1 is directed to conduit 2 and passed through a control valve to producelower pressure steam 4. Conduit 4 may comprise lower pressure steam witha quality less than or equal to unity, depending on the temperature andpressure conditions of steam 2. Steam 4 is passed through one side of aheat exchange device 5 wherein, steam 4 is superheated by indirectcontact with the remaining portion of the high pressure steam flowingvia conduit 3 to the other side of heat exchange device 5. Superheatedlower pressure steam emerges from heat exchange device 5 via conduit 6.Condensate and any remaining vapor fraction of the high pressure steamexits via conduit 7. A fraction of superheated steam 6 may be removedfrom the process via conduit 10 and the remainder of steam 6 is passedon to a steam driven turbine 8 to provide motive force to produceelectrical or mechanical energy. The exhaust from turbine 8 exits viaconduit 9.

In the embodiment set forth in FIG. 2, a portion of the high pressuresteam flowing in conduit 1 is directed to conduit 2 and passed through acontrol valve to produce lower pressure steam 4. Conduit 4 may compriselower pressure steam with a quality less than or equal to unity,depending on the temperarture and pressure conditions of steam 2.

Liquid water is separated from the lower pressure vaporous steam ingas-liquid segregation zone 7. Lower pressure steam, essentially freefrom liquid water, exits gas-liquid segregation zone 7 via conduit 5,while liquid water is removed via conduit 6. Removal of liquid water maybe accomplished by any means known in the art, for example as describedin “phase Segregation”, Chapter 3, pp. 129-148, L. J. Jacobs and W. R.Penney, in Handbook of Separation Process Technology, R. W. Rousseau,ed., Wiley & Sons, 1987, including knockout pots, pipe separators, meshpads, centrifugal vanes, tangential entry separators, demister orcoalescer pads, wavy plates, packing, cyclone or venturi scrubbers,electrostatic precipitators, and the like.

Steam 5 is passed through one side of a heat exchange device 8 wherein,steam 5 is superheated by indirect contact with the remaining portion ofthe high pressure steam flowing via conduit 3 to the other side of heatexchange device 8. Superheated, lower pressure steam emerges from heatexchange device 8 via conduit 10. Condensate and any remaining vaporfraction of the high pressure steam exits via conduit 9. A fraction ofSuperheated steam 10 may be removed from the process via conduit 13 andthe remainder of steam 10 is passed on to steam driven turbine 11 toprovide motive force to produce electrical or mechanical energy. Theexhaust from turbine 11 exits via conduit 12.

In the embodiment set forth in FIG. 3, a portion of the high pressuresteam flowing in conduit 1 is directed to conduit 2 and passed through acontrol valve to produce lower pressure steam 4. Conduit 4 may compriselower pressure steam with a quality less than or equal to unity,depending on the temperarture and pressure conditions of steam 2.

Liquid water is separated from the lower pressure vaporous steam ingas-liquid segregation zone 7. Lower pressure steam, essentially freefrom liquid water, exits gas-liquid segregation zone 7 via conduit 5,while liquid water is removed via conduit 6. Steam 5 is passed throughone side of a heat exchange device 8 wherein, steam 5 is superheated byindirect contact with the remaining portion of the high pressure steamflowing via conduit 3 to the other side of heat exchange device 8.Superheated lower pressure steam emerges from heat exchange device 8 viaconduit 10. Condensate and any remaining vapor fraction of the highpressure steam exits via conduit 9. A fraction of superheated steam 10may be removed from the process via conduit 20 and the remainder ofsteam 10 is passed on to steam driven turbine 11 to provide motive forceto produce electrical or mechanical energy. The exhaust from turbine 11exits via conduit 12 and is condensed in condenser 13 to producecondensate 14. Condensate 14, stream 9, and condensate 6, may becombined with make-up water 15 to produce a boiler feed water stream 16.

Steam generating zone 17 may comprise steam generating heat exchangers(i.e., boilers) wherein heat is transferred from a heating medium toboil water and boiler feed water exchangers. Heat transfer within steamgenerating zone 17 may occur by radiant and/or convective heat transfermechanisms. Heat is transferred into zone 17 via stream 19. Stream 19may represent heat flow such as, for example, from a chemical reaction,as described hereinabove, or a flow of matter. The use of multiple heatexchangers is contemplated to be within the scope of the instantinvention. High pressure steam generated within zone 17 exits viaconduit 1. A fraction of the steam generated in zone 17 may be directedto conduit 18 to exit the process.

In the embodiment set forth in FIG. 4, a portion of the high pressuresteam flowing in conduit 1 is directed to conduit 2 and passed throughsteam turbine 20 to produce lower pressure steam 4 and electricity.Conduit 4 may comprise a lower pressure steam with a quality less thanor equal to unity, depending on the temperature and pressure conditionsof steam 2.

Liquid water is separated from the lower pressure vaporous steam ingas-liquid segregation zone 7. Lower pressure steam, essentially freefrom liquid water, exits gas-liquid segregation zone 7 via conduit 5,while liquid water is removed via conduit 6. Steam 5 is passed throughone side of a heat exchange device 8 wherein, steam 5 is superheated byindirect contact with the remaining portion of the high pressure steamflowing via conduit 3 to the other side of heat exchange device 8.Superheated lower pressure steam emerges from heat exchange device 8 viaconduit 10. Condensate and any remaining vapor fraction of the highpressure steam exits via conduit 9. A fraction of lower pressuresuperheated steam 10 may be removed from the process via conduit 21 andthe remainder of steam 10 is passed on to steam driven turbine 11 toprovide motive force to produce electrical or mechanical energy. Theexhaust from turbine 11 exits via conduit 12 and is condensed incondenser 13 to produce condensate 14. Condensate 14, stream 9, andcondensate 6, may be combined with make-up water 15 to produce a boilerfeed water stream 16.

Steam generating zone 17 may comprise steam generating heat exchangers(i.e., boilers) wherein heat is transferred from a heating medium toboil water, and boiler feed water exchangers. Heat transfer within steamgenerating zone 17 may occur by radiant and/or convective heat transfermechanisms. Heat is transferred into zone 17 via stream 19. Stream 19may represent heat flow such as, for example, from a chemical reaction,as described hereinabove, or a flow of matter. The use of multiple heatexchangers is contemplated to be within the scope of the instantinvention. High pressure steam generated within zone 17 exits viaconduit 1. A fraction of the high pressure steam generated in zone 17may be directed to conduit 18 to exit the process.

In the embodiment set forth in FIG. 5, a high pressure steam flowing inconduit 1 is directed to one side of heat exchange device 2, such thatheat is transferred to lower pressure steam 9 on the other side ofdevice 2 to produce superheated steam 10. Condensate and any remainingvapor fraction of the high pressure steam exits device 2 via conduit 3.Condensate 3, may be combined with make-up water 4 to produce a boilerfeed water stream 19 to steam generating zone 5.

High pressure steam generating zone 5 may comprise steam generating heatexchangers (i.e., boilers) wherein heat is transferred from a heatingmedium to boil water, and boiler feed water exchangers. Heat transferwithin steam generating zone 5 may occur by radiant and/or convectiveheat transfer mechanisms. Heat is transferred into zone 5 via stream 6.Stream 6 may represent heat flow, for example from a chemical reaction,or a flow of matter. The use of multiple heat exchangers is contemplatedto be within the scope of the instant invention. High pressure steamgenerated within zone 5 exits via conduit 1. A fraction of high pressuresteam generated in zone 5 may be directed to conduit 7 to exit theprocess.

A fraction of superheated steam 10 may be removed from the process viaconduit 20 and the remainder of steam 10 is passed on to steam driventurbine 11 to provide motive force to produce electrical or mechanicalenergy. The exhaust from turbine 11 exits via conduit 12 and iscondensed in condenser 13 to produce condensate 14. Condensate 14 may becombined with make-up water 15 to produce a boiler feed water stream 16for lower pressure steam generating zone 8.

Steam generating zone 8 may comprise steam generating heat exchangers(i.e., boilers) wherein heat is transferred from a heating medium toboil water, and boiler feed water exchangers. Heat transfer within steamgenerating zone 8 may occur by radiant and/or convective heat transfermechanisms. Heat is transferred into zone 8 via stream 18. Stream 18 mayrepresent heat flow such as, for example, from a chemical reaction, asdescribed hereinabove, or a flow of matter. The use of multiple heatexchangers is contemplated to be within the scope of the instantinvention. High pressure steam generated within zone 8 exits via conduit1. A fraction of the steam generated in zone 8 may be directed toconduit 17 to exit the process.

EXAMPLES

General—A better understanding of the invention is provided withparticular reference to the examples given below. For Examples 1-9 andComparative Examples 1-3, heat and material balance calculations werecarried out to illustrate the aspects of the instant invention byprocess simulation software using methods described in “Program ComputesSteam Rates and Properties”, by V. Ganaphthy in Hydrocarbon Processing,November 1988, pp. 105-108, and in standard engineering texts such as,for example, Perry's Handbook of Chemical Engineering, 6^(th) ed., NewYork, McGraw Hill, 1984. Also, unless expressly stated otherwise, itshould be understood that the high pressure steam or heat used togenerate the high pressure steam, as set forth in the Examples andComparative Examples, may be obtained by recovering heat from anyheat-producing chemical process as described hereinabove such as, forexample, the production of syngas by gasification of carbonaceousmaterials or by steam reforming of methane, the water-gas shiftreaction, hydrogenation of carbon monoxide or carbon dioxide to producemethanol, production of ammonia by hydrogenation of nitrogen, or acombination of one or more of these processes.

Comparative Example 1

100,000 kg/hr of saturated high pressure steam at 131 bara and 331.45°C. is fed to a steam turbine with an outlet pressure of 0.12 bara and amechanical efficiency of 86.5% to produce electricity. The turbinegenerates 22.3 MW, with a steam quality of 69.3% at the outlet of theturbine.

Examples 1-5

Examples 1-5 illustrate the effect on turbine outlet steam quality bychanging the pressure to which the high pressure inlet steam is reducedas per FIG. 1 of the instant invention. 100,000 kg/hr of saturated highpressure steam at 131 bara and 331.45° C. is divided and a portion isreduced in pressure. The resulting lower pressure steam is subjected toheat exchange with the remaining portion of high pressure steam. Theapproach temperature in the heat exchanger is 5° C., i.e., thesuperheated lower pressure steam temperature is 326.45° C. in all cases.The superheated lower pressure steam is fed to a steam turbine with anoutlet pressure of 0.12 bara and a mechanical efficiency of 86.5% toproduce electricity. Table 1 shows results per the instant invention forvarious lower pressure values. TABLE 1 Effect of Pressure Lower Amountof Turbine Pressure Lower P Steam Degrees Outlet Steam, (thousandsSuperheat, Electricity, Steam bara Kg/hr) ° C. MW Quality Example 1 65.579.2 45.1 18.8 79.5% Example 2 56.2 77.6 55.1 18.3 81.0% Example 3 42.475.4 72.6 17.5 83.3% Example 4 28.6 73.6 95.2 16.4 86.2% Example 5 14.672.2 128.7 14.7 90.5%

Comparative Example 2

100,000 kg/hr of saturated high pressure steam at 131 bara and 331.45°C. is fed to a steam turbine with an outlet pressure of 0.12 bara and amechanical efficiency of 86.5% to produce electricity. The turbinegenerates 22.3 MW, with a steam quality of 69.3% at the outlet of theturbine. The wet steam from the outlet of the turbine is condensed atthe saturation temperature of 0.12 bara steam (49.6° C.), giving up165.1 GJ/hr during the condensation process. The condensed steam ispumped back up to 131 bara and subjected to heat transfer where 245.3GJ/hr are transferred to produce 100,000 kg/hr of saturated highpressure steam at 131 bara and 331.45° C., completing the steam cycle.The overall efficiency, E, of the steam cycle is 32.7%, where:E=(heat in−condensing duty)/heat in=(245.3 GJ/hr−165.1 GJ/hr)/245.3GJ/hr

Example 6

Example 6, following the nomenclature of FIG. 3, illustrates the overallefficiency of a steam cycle. Heat input into steam generating zone 17via conduit 19 is 245.3 GJ/hr as in Comparative Example 2. 112,350 kg/hrof liquid water at 49.5° C., is boiled in heat transfer zone 17 toproduce 112,350 kg/hr of saturated high pressure steam at 131 bara and331.45° C. in conduit 1. 17,550 Kg/hr is diverted via conduit 3, theremainder of 94,800 kg/hr passes via conduit 2 and is flashed across avalve to produce saturated steam at 42.4 bara, 253.8° C., 91.8% quality.The resulting lower pressure steam is divided into 7800 kg/hr ofsaturated liquid in conduit 6 and 87,000 kg/hr of saturated vapor inconduit 5. Conduit 5 subjected to heat exchange with conduit 3 inexchanger 8. The approach temperature in the heat exchanger is 5° C.,producing superheated lower pressure steam temperature at 326.45° C.,42.4 bara in conduit 10 and condensed high pressure steam at 331.45° C.in conduit 9. The superheated lower pressure steam in conduit 10 is fedto steam turbine 11 with an outlet pressure of 0.12 bara and amechanical efficiency of 86.5% to produce 20.2 MW of electricity. Thesteam at the outlet of the turbine, conduit 12, has a quality of 83.3%.Conduit 12 is fully condensed in exchanger 13 by removal of 172.8 GJ/hrof energy, and exits as saturated liquid stream 14 at 49.5° C. Streams14, 9, and 6 are combined and pumped back up to 131 bara, subjected tosteam generating zone in zone 17 where 245.3 GJ/hr are transferred viaconduit 19 to produce 112,350 kg/hr of saturated high pressure steam at131 bara and 331.45° C., completing the steam cycle. The overallefficiency, E, of the steam cycle is 29.6%. This efficiency is 90.5% ofthe efficiency reported in Comparative Example 2, but with a much highersteam turbine outlet quality, as per the objective of the instantinvention.

Example 7

Example 7, following the nomenclature of FIG. 4, illustrates the overallefficiency of a steam cycle. Heat input into steam generating zone 17via conduit 19 is 245.3 GJ/hr as in Comparative Example 2. 115,290 kg/hrof liquid water via conduit 16 is boiled in heat transfer zone 17 toproduce 115,290 kg/hr of saturated high pressure steam at 131 bara and331.45° C., exiting via conduit 1. 16,410 Kg/hr is diverted via conduit3, the remainder of 98,880 kg/hr passes via conduit 2 and is expanded insteam turbine 20 with a mechanical efficiency of 86.5% to produce 4.4 MWof electricity, and saturated steam at 42.4 bara, 253.8° C., 82.3%quality. The resulting lower pressure steam is divided into 17510 kg/hrof saturated liquid in conduit 6 and 81,370 kg/hr of saturated vapor inconduit 5. Conduit 5 subjected to heat exchange with conduit 3 inexchanger 8. The approach temperature in the heat exchanger is 5° C.,producing superheated lower pressure steam temperature at 326.45° C.,42.4 bara in conduit 10 and condensed high pressure steam at 331.45° C.in conduit 9. The superheated lower pressure steam in conduit 10 is fedto steam turbine 11 with an outlet pressure of 0.12 bara and amechanical efficiency of 86.5% to produce 18.8 MW of electricity. Thesteam at the outlet of the turbine, conduit 12, has a quality of 83.3%.Conduit 12 is fully condensed in exchanger 13 by removal of 161.6 GJ/hrof energy, and exits as saturated liquid stream 14 at 49.5° C. Streams14, 9, and 6 are combined and pumped back up to 131 bara, subjected tosteam generating zone in zone 17 where 245.3 GJ/hr are transferred viaconduit 19 to produce 115,290 kg/hr of saturated high pressure steam at131 bara and 331.45° C., completing the steam cycle. The overallefficiency, E, of the steam cycle is 34.1%. This efficiency is 104.2% ofthe efficiency reported in Comparative Example 2, and with a much highersteam turbine outlet quality, as per the objective of the instantinvention. Furthermore, the total electricity production of 23.2 MWexceeds that of Comparative Example 2 (22.3 MW) by 4.1%.

Comparative Example 3

100,000 kg/hr of saturated high pressure steam at 41.4 bara and 252.36°C. is fed to a steam turbine with an outlet pressure of 0.12 bara and amechanical efficiency of 86.5% to produce electricity. The turbinegenerates 20.75 MW, with a steam quality of 77.4% at the outlet of theturbine. The wet steam from the outlet of the turbine is condensed atthe saturation temperature of 0.12 bara steam (49.6° C.), giving up184.5 GJ/hr during the condensation process. The condensed steam ispumped back up to 41.4 bara and subjected to heat transfer where 259.3GJ/hr are transferred to produce 100,000 kg/hr of saturated highpressure steam at 41.4 bara and 252.36° C., completing the steam cycle.The overall efficiency, E, of the steam cycle is 28.9%, where:E=(heat in−condensing duty)/heat in=(259.3 GJ/hr−784.5 GJ/hr)/259.3GJ/hr

Example 8

Example 8, following the nomenclature of FIG. 4, illustrates the overallefficiency of a steam cycle. Heat input into steam generating zone 17via conduit 19 is 259.3 GJ/hr as in Comparative Example 3. 104,860 kg/hrof liquid water via conduit 16 is boiled in heat transfer zone 17 toproduce 104,860 kg/hr of saturated high pressure steam at 41.4 bara and252.36° C., exiting via conduit 1. 8,070 Kg/hr is diverted via conduit3, the remainder of 96,790 kg/hr passes via conduit 2 and is expanded insteam turbine 20 with a mechanical efficiency of 86.5% to produce 6.00MW of electricity, and saturated steam at 10.34 bara, 181.35° C., 90%quality. The resulting lower pressure steam is divided into 9,660 kg/hrof saturated liquid in conduit 6 and 87,130 kg/hr of saturated vapor inconduit 5. Conduit 5 subjected to heat exchange with conduit 3 inexchanger 8. The approach temperature in the heat exchanger is 5° C.,producing superheated lower pressure steam at 247.36° C., 10.34 bara inconduit 10 and condensed high pressure steam at 252.36° C. in conduit 9.The superheated lower pressure steam in conduit 10 is fed to steamturbine 11 with an outlet pressure of 0.12 bara and a mechanicalefficiency of 86.5% to produce 15.2 MW of electricity. The steam at theoutlet of the turbine, conduit 12, has a quality of 88.1%. Conduit 12 isfully condensed in exchanger 13 by removal of 173.34 GJ/hr of energy,and exits as saturated liquid stream 14 at 49.5° C. Streams 14, 9, and 6are combined and pumped back up to 41.4 bara, subjected to steamgenerating zone in zone 17 where 259.3 GJ/hr are transferred via conduit19 to produce 104,860 kg/hr of saturated high pressure steam at 41.4bara and 252.36° C., completing the steam cycle. The overall efficiency,E, of the steam cycle is 29.5%. This efficiency is 102.2% of theefficiency reported in Comparative Example 2, and with a much highersteam turbine outlet quality, as per the objective of the instantinvention. Furthermore, the total electricity production of 21.21 MWexceeds that of Comparative Example 2 (20.75 MW) by 2.2%.

Example 9

Example 9 illustrates the embodiment of the invention as set forth inFIG. 5. A syngas stream from an oxygen blown gasifier comprising 57,242lbmole/hr of carbon monoxide, hydrogen, water, and carbon dioxide issubjected to a water gas shift reaction to produce a hot shifted syngas.A portion of the heat of reaction is removed in heat transfer zone 5 bygenerating 115,693 kg/hr of 37.6 bara steam at 246.7° C. The syngas isfurther cooled in heat transfer zone 8 to produce 455,475 kg/hr of 4.5bara steam at 147.6° C. The lower pressure steam exits zone 8 viaconduit 9 and is superheated in exchanger 2 by heat exchange with 62,600kg/hr of high pressure steam in conduit 1. The approach temperature inexchanger 2 is 5° C. 455,475 kg/hr of superheated steam at 241.65° C. ispassed via conduit 10 through turbine 11 (86.5% efficiency) to generate66.7 MW of power. The outlet quality of the steam in conduit 12 is92.8%. This compares to a power generation of 59.9 MW, with an outletquality of 86% if steam 9 had not been superheated.

1. A process for the preparation of superheated steam, comprising: (a)recovering heat from at least one chemical process to produce a highpressure steam; (b) reducing the pressure of a portion of said highpressure steam of step (a) to produce a lower pressure steam and aremaining portion of said high pressure steam; and (c) transferring heatfrom at least a fraction of said remaining portion of said higherpressure steam of step (b) to said lower pressure steam to produce asuperheated steam from said lower pressure steam.
 2. The processaccording to claim 1 wherein said remaining portion of said highpressure steam and said lower pressure steam have a difference in watersaturation temperature of about 40° C. to about 250° C.
 3. The processaccording to claim 1 wherein said high pressure steam is generated byrecovering heat from at least one chemical process selected from partialoxidation, carbonylation, hydrogenation, water-gas shift reaction, steamreforming, and homologation.
 4. The process according to claim 3 whereinsaid at least one chemical process comprises gasification ofcarbonaceous materials to produce synthesis gas, hydrogenation of carbonmonoxide or carbon dioxide to produce methanol, partial oxidation ofethylene to produce ethylene oxide, steam reforming of methane toproduce synthesis gas, partial oxidation of methanol to produceformaldehyde, production of Fischer-Tropsch hydrocarbons or alcoholsfrom synthesis gas, ammonia production from hydrogen and nitrogen,autothermal reforming of carbonaceous feedstocks to produce synthesisgas, hydrogenation of dimethyl terephthalate to cyclohexanedimethanol,carbonylation of methanol to acetic acid, a water-gas shift reaction toproduce hydrogen and carbon dioxide from carbon monoxide and water, or acombination thereof.
 5. The process according to claim 4 wherein saidchemical process comprising gasification of carbonaceous materials toproduce synthesis gas.
 6. The process according to claim 1 wherein saidrecovering heat of step (a) is by radiant heat exchange, convective heatexchange, or a combination thereof.
 7. The process according to claim 6wherein said recovering heat is by radiant heat exchange.
 8. The processaccording to claim 1 wherein said high pressure steam of step (a) issaturated or superheated and has a pressure of about 4 to about 140bara.
 9. The process according to claim 8 wherein said high pressuresteam of step (a) has a pressure of about 20 to about 120 bara.
 10. Theprocess according to claim 1 wherein said pressure reducing of step (b)comprises expanding said said portion of said high pressure steamthrough a valve, a turbine, or a combination thereof.
 11. The processaccording to claim 1 wherein said superheated steam is passed to a steamturbine.
 12. The process according to claim 11 wherein said steamturbine produces an outlet steam having a quality of about 80 percent toabout 100 percent.
 13. The process according to claim 1 wherein saidtransferring of heat of step (c) is performed with a shell and tube heatexchanger, plate and frame exchanger, spiral exchanger, plate-finexchanger, or a combination thereof.
 14. The process according to claim1 wherein said superheated steam and said remaining portion of saidhigher pressure steam have an approach temperature of about 1 to about20° C.
 15. The process according to claim 14 wherein said superheatedsteam and said remaining portion of said higher pressure steam have anapproach temperature of about 1 to about 10° C.
 16. A process for thepreparation of superheated steam, comprising: (a) reacting acarbonaceous material with oxygen, water, or carbon dioxide to produceheat and a syngas stream comprising hydrogen, carbon monoxide, andcarbon dioxide; (b) recovering said heat to produce a high pressuresteam; and (c) transferring heat from at least a fraction of said highpressure steam of step (b) to a lower pressure steam by indirect heatexchange to produce a superheated steam from said lower pressure steam.17. The process according to claim 16 wherein said carbonaceous materialcomprises methane, petroleum residuum, carbon monoxide, coal, coke,lignite, oil shale, oil sands, peat, biomass, petroleum refiningresidues, petroleum cokes, asphalts, vacuum resid, heavy oils, orcombinations thereof.
 18. The process according to claim 17 wherein saidcarbonaceous material of step (a) is reacted in a gasifier, partialoxidizer, or reformer.
 19. The process according to claim 18 whereinsaid carbonaceous material comprises methane and is reacted with waterin a reformer.
 20. The process according to claim 18 wherein saidcarbonaceous material comprises carbon monoxide and is reacted withwater in a water-gas shift reaction.
 21. The process according to claim18 wherein said carbonaceous material comprises coal or petroleum cokeand is reacted with oxygen in a gasifier.
 22. The process according toclaim 21 wherein said lower pressure steam is generated by reducing thepressure of a portion of said high pressure steam.
 23. The processaccording to claim 22 wherein said pressure reducing comprises expandingsaid portion of said high pressure steam through a valve, a turbine, ora combination thereof.
 24. The process according to claim 21 whereinsaid lower pressure steam is generated by recovery of heat from at leastone chemical process selected from a water-gas shift reaction,hydrogenation of carbon monoxide or carbon dioxide to produce methanol,hydrogenation of nitrogen to produce ammonia, carbonylation of methanolto produce acetic acid, a Fischer-Tropsch process, production of alkylformates from carbon monoxide and alcohols, and combinations thereof.25. The process according to claim 24 wherein said chemical process issaid water-gas shift reaction, hydrogenation of carbon monoxide orcarbon dioxide to produce methanol, hydrogenation of nitrogen to produceammonia, or a combination thereof.
 26. The process according to claim 16wherein said recovering heat of step (a) is by radiant heat exchange,convective heat exchange, or a combination thereof.
 27. The processaccording to claim 26 wherein said recovering heat is by radiant heatexchange.
 28. The process according to claim 16 wherein said highpressure steam of step (a) is saturated or superheated and has apressure of about 4 to about 140 bara.
 29. The process according toclaim 28 wherein said high pressure steam of step (a) has a pressure ofabout 20 to about 120 bara.
 30. The process according to claim 16wherein said superheated steam is passed to a steam turbine.
 31. Theprocess according to claim 30 wherein said steam turbine produces anoutlet steam having a quality of about 80 to 100 percent.
 32. Theprocess according to claim 16 wherein said transferring of heat of step(c) is performed with a heat shell and tube heat exchanger, plate andframe exchanger, spiral exchanger, compact plate-fin exchangers, or acombination thereof.
 33. The process according to claim 16 wherein saidsuperheated steam and said remaining portion of said higher pressuresteam have an approach temperature of about 1 to about 20° C.
 34. Theprocess according to claim 33 wherein said superheated steam and saidremaining portion of said higher pressure steam have an approachtemperature of about 1 to about 10° C.
 35. A process for driving a steamturbine, comprising: (a) reacting a carbonaceous material with oxygen ina gasifier to produce heat and a syngas stream comprising hydrogen,carbon monoxide, and carbon dioxide; (b) recovering said heat to producea high pressure steam; (c) transferring heat from at least a fraction ofsaid high pressure steam of step (b) to a lower pressure steam byindirect heat exchange to produce a superheated steam from said lowerpressure steam; and (d) passing said superheated steam to a steamturbine.
 36. The process according to claim 35 wherein said lowerpressure steam is generated by reducing the pressure of a portion ofsaid high pressure steam, by recovery of heat from at least one chemicalprocess selected from a water-gas shift reaction, hydrogenation ofcarbon monoxide or carbon dioxide to produce methanol, hydrogenation ofnitrogen to produce ammonia, carbonylation of methanol to produce aceticacid, a Fischer-Tropsch process, production of alkyl formates fromcarbon monoxide and alcohols, and combinations thereof, or by acombination thereof.
 37. The process according to claim 36 wherein saidreducing pressure comprises expanding said portion of said high pressuresteam through a valve, a turbine, or combination thereof.
 38. Theprocess according to claim 36 wherein said chemical process comprisessaid water-gas shift reaction, hydrogenation of carbon monoxide orcarbon dioxide to produce methanol, hydrogenation of nitrogen to produceammonia, or a combination thereof.
 39. The process of claim 38 whereinsaid chemical process comprises hydrogenation of carbon monoxide orcarbon dioxide to produce methanol.
 40. The process according to claim35 wherein said recovering heat of step (b) is by radiant heat exchange,convective heat exchange, or a combination thereof.
 41. The processaccording to claim 40 wherein said recovering heat is by radiant heatexchange.
 42. The process according to claim 35 wherein said highpressure steam of step (a) has a pressure of about 20 to about 120 bara.43. The process according to claim 35 wherein said steam turbine drivesa generator to produce electricity or drives a gas compressor.
 44. Theprocess according to claim 43 wherein said steam turbine produces anoutlet steam having a quality of about 80 percent to about 100 percent.